Distinguishing ecological constraints from human activity in species range fragmentation: the case of Cross River gorillas

Abstract

The geographic range of many species has been reduced and fragmented by human impact, and ever more species live in human-dominated landscapes where they are confined to small and often suboptimal refuge areas. A detailed understanding of the causation of species' persistence and disappearance is crucial to inform management of which interventions are likely to be most effective. Yet this information is often not available to decision makers and may, in the worst case, lead to erroneous management decisions. To clarify whether Cross River gorilla Gorilla gorilla diehli (CRG) occurrence is restricted due to ecological constraints or human disturbance, we collected extensive field data on food availability, habitat structure, human activity and wildlife abundance, which we related to CRG occurrence. We also related spatial variation in hunting pressure to human density, household forest use and topography. Our results clearly show that CRG are currently confined to refuge areas because of ongoing detrimental human activities and not because of lack of food resources. Current hunting pressure is driven by human population pressure, accessibility and socioeconomic conditions influencing household dependence on forest. A substantial amount of ecologically suitable but currently unoccupied habitat could potentially carry a much larger CRG population. Conservation management should therefore focus on reducing hunting and disturbance of CRG. In contrast, ecological restoration would not improve CRG living conditions. Our field and analytical approach is widely applicable to the rapidly increasing number of species inhabiting heavily human-influenced landscapes for identifying appropriate management interventions for their protection.